I'm a little confused on the correct way to measure for and set the dialnorm metadata value when creating an AC3 for delivery to a client. Here's a scenario I just went through:

A month or two back, I did a 5.1 student film mix where the delivery requirements were just the trimmed/conformed stems. AC3 creation was to be handled by another department that was creating the graduation ceremony DVD with all the finished films on it.

Fast-forward to the graduation ceremony - the entire batch of final films is quiet as hell, probably in the range of 9dB below where everyone should be hearing them. The audience was straining to hear dialogue and even the big full-scale moments are registering like a Powerpoint presentation. A few mixers from the other films on that DVD that were in attendance confirmed that the same thing had happened to their mixes. It sucked.

As a few short films that had aired earlier in the ceremony (ones where sound people had created the AC3s) sounded fine (e.g. calibrated for 85), and I can't imagine whoever was running the booth just suddenly trimmed the entire playback system down in time for the main event, I suspect it was a problem with AC3 creation and the decode.

**

A few weeks ago, I do another mix where I'm responsible for delivery all the way through the AC3..

Disclaimer: this is my understanding of how the dialnorm value is handled on playback, and it's here that I would love corrections and notes. I hope that I am at least close to the truth.

The dialnorm parameter is used in the
decoding process to adjust the mix's
level appropriately for how the user's
playback system is set up. The
dialnorm value itself is, in
professional cases, automatically
determined by a Dolby hardware
box/plugin whose algorithm can
intelligently separate dialogue from
the other sounds in the mix and spit
out an average dialogue level for you.
You key this in to your encoding
software, make your AC3, and go.

What happens at the time of decode is
that the entire mix will be trimmed to
bring the encoded mix's specified dial
level to whatever -27dbSPL is on the
user's playback system. So if you key
in a dialnorm value of -23, the whole
mix is going to get ducked 4dB on
playback for an unattenuated system.
If the user's turned his system down
by 6dB so he can have a conversation
with his buddy while the movie's on,
your mix will be dropped 10dB.

The decoder will not automatically
boost the original signal no matter
what the dialnorm was set to.

To avoid stuff playing back too quietly again, I decide to simply set the dialnorm metadata value at -31 (e.g. "don't adjust anything") -- even though I had mixed all the film's dialogue to average between -20 and -23. I was just scared of the decoder dropping my mix due to anything being set incorrectly and didn't want to take any chances. Also, delivery was happening at the 11th hour due to a last minute picture cut, so there wasn't time to burn a DVD and test playback before shipping this thing.

Was this the right thing to do?

Have you experienced similar horror stories?

And how should setting the dialnorm -- and playing back the finished DVD -- go in a perfect world?

I'm still pretty new to deliveries and would love to hear this board's experiences. Maybe we can make this into a community post aftwards.

1 Answer
1

In my experience, if I'm reading you right, is that you're experiencing the discrepancy between a theatrical and a DVD mix, or rather, the professional versus consumer differences. Think of it sort of like the -10 versus +4 of line level. On a home theater system calibrated properly, when I boosted the amp's playback level to 100, it sounded proper for a -20dB mix put on a DVD- But any lower (lower, like to the amp level used when watching other DVDs or TV) it sounded too quiet. Made me wonder why when I pop a DVD I bought at the store, I have to lower the volume a lot to get a comparable -20dB playback level, because otherwise it's too loud. When preparing a mix for DVD/Web (consumer playback), I boost the stems by 6dB and engage a brickwall at about -3dB or so like the L2007 or Maxim - nothing to degrade the signal but just as a catch-all. And then I make automated adjustments as needed That seems to yield proper playback levels similar to DVDs you find in the store, and similar to the playback levels I hear on Hulu etc. And it turns out a lot of DVDs/BluRays have "remixed" printmasters that are boosted in level, compressed in dynamics, for optimal playback in a consumer environment - most of the times it sounds pretty transparent, but on some action shows when heard on headphones, you can hear they slammed it hard against a limiter (this is my beef with them using the marketing ploy "Master Audio blah blah the same mix heard on the stage" or "at the theater" - well, NOT quite true - uncompressed fidelity, yes... but byte-per-byte frequency and dynamics representation of what was used to strike the 35mm print, probably not).

But when I've used the regular theatrical -20dB mix for DVDs or web, without that 6dB boost and dynamics control, it sounds super low. This is just my own experience though, and what research has led me to do with my own work. There seems to be a somewhat of a "dark art" to consumer printmastering practices, have had a hard time finding any white paperish information or documentation about it. The +6dB to stems and limiting is about all I've managed to find.

And, you are correct... that's what dialnorm does in AC3, but only so long as you know what you mixed to and enter the proper value to compensate for that level. The other part of it too is determing the LEQ(a) loudness of the Center dialogue track through a Dolby LM100 hitting a loudness target of -27dB. If using the Phasescope over a stereo mix bus, I believe the target to hit is -24dB for an equivalent -27dB true Center via the LM100 (because of the phantom center summing). My understanding, and somebody please correct me if I'm wrong, is that whatever number you calibrate to via the LM100 is what the dialnorm value is for the metadata (usually -27, but some places like Discovery want -24).